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The 49ers have plenty of experience rolling with a Plan B at the quarterback position in recent years, and it looks like they'll have to do so again in Week 8, as Brock Purdy is in the concussion protocol and appears unlikely to play Sunday against the Bengals.

Obviously as of Wednesday afternoon, Purdy hasn't been ruled out yet, and he's got three full days to get clearance. However, recent history with the concussion protocol suggests that his chances aren't great, as Adam Schefter notes: Brock Purdy is now unlikely to play Sunday vs. the Bengals based on this trend: No NFL player placed into concussion protocol this season has played the same week. The last player to be in concussion protocol who played the same week was 2022, when Kenny Pickett had a concussion.

Purdy himself, of course, only played last season after two injuries at the QB position for the 49ers – first to Trey Lance early in the season, and then to Jimmy Garoppolo toward the end of the season. Purdy filled in well, ultimately earning the starting job, and he's gone 10-2 as a starter with 24 touchdowns, seven interceptions, and 8.4 yards per attempt in 12 starts since. 

Sam Darnold has some pretty big shoes to fill, in other words, though the nice thing is, this 49ers offense under Kyle Shanahan has been better than nearly any at making life easy for quarterbacks. Since Shanahan took over as head coach in 2017, 49ers quarterbacks have the eighth-best passer rating in the league, while ranking second in yards per attempt and 11th in touchdown rate. And they've done that with few guys any NFL coach would consider high-quality starters. 

Darnold hasn't looked like a particularly high-quality option over the years, of course, and we should expect a downgrade for the 49ers offense as a whole if he has to start in Purdy's absence. Darnold hasn't completed more than 60% of his passes since 2019, though he did at least show some signs of improvement in 2022 when he started six games for the Panthers, sporting a career-best 5.0% touchdown rate and 8.2 yards per attempt. The 49ers saw enough to go out and get Darnold to back Purdy up, while trading former first-round pick Trey Lance this preseason. 

Which is to say that, while I don't expect Darnold to be great, the 49ers offense might make him look pretty decent. It's a downgrade for the offense as a whole, but as long as Darnold can make the relatively easy passes Shanahan dials up to playmakers like Christian McCaffrey, George Kittle, and Brandon Aiyuk, things should be okay – all three of those guys are among the best after-the-catch playmakers in the NFL, so they figure to do a lot of the heavy lifting. 

For what it's worth, the line in the 49ers game moved a few points with the news that Purdy is in the concussion protocol: They were six-point favorites initially, but that dropped to 3.5 points after the injury was announced. That's not a gigantic move for the loss of a starting quarterback, which reflects Purdy's struggles over the past few weeks, plus some lingering skepticism about whether he is elevating the offense or vice versa. 

Still, it's a downgrade, and it makes sense. We've seen Purdy play much better than Darnold, and even in a better situation, I wouldn't be surprised at all to see Darnold really struggle. He's never been great with pressure, and the Bengals have been one of the better teams at rushing the passer with just four or five players, ranking 10th or better in pressure rate in those situations. That's a tough thing for any QB to deal with, but especially one like Darnold, who has a tendency to panic and make bad decisions when pressured. 

McCaffrey is still the No. 1 running back in my rankings for Week 8, and I wouldn't be surprised if they leaned on him even more in the running game to help Darnold out. The bigger question comes with Aiyuk and Kittle. I'm still ranking both as starters, but it's on the lower end of the range – Kittle is TE8, while Aiyuk falls to WR21, just ahead of Garrett Wilson, who is dealing with similarly unfortunate QB play in New York.

So, again, it's not a total burial of the 49ers offensive weapons. The scheme should help Darnold, and each of those guys is perfectly capable of housing any competently thrown pass at basically any point in a game. It's just that the chances of any given pass being competently thrown goes down with Darnold replacing Purdy.